1. Field of the Invention
The present invention relates to a medical knife having a sharp tip, and more specifically, to a medical knife whose durability is enhanced when it pierces tissue.
2. Description of the Related Art
A medical knife is ordinarily used in, for example, an ophthalmic surgery, to form an incision wound to an eyeball. There have been provided various types of medical knives. Among them, there is a medical knife which has a sharp tip at the extreme end thereof, is formed in an approximately rhombic shape using the tip as its apex, and has a cutting edge formed up to the widest portion of the rhombic shape.
As an example of the medical knives, there is a medical knife having a cutting edge formed using a sharp tip formed at the extreme end of a blade portion as its apex. The knife has a first slanting surface, which slants from the cutting edge inwardly upwardly of the blade portion in the thickness direction of the knife on a boundary as a surface including the cutting edge, a second slanting surface formed continuously to the first slanting surface, and an uppermost flat surface formed as an upper surface. Further, the knife has a lower side slanting surface, which slants from the cutting edge inwardly of the blade portion in the thickness direction of the knife, and a flat surface formed continuously to the lower side slanting surface under the above boundary (refer to, for example, Japanese Patent Application Laid-Open No. 2001-238890).
The medical knife has an approximately rhombic planar shape, and the cutting edge is formed up to the widest portion of the rhombic shape. That is, the medical knife is formed in the rhombic shape having the widest portion necessary to form a target incision wound, and the cutting edge is formed along the sides of the knife between the tip and the widest portion.
Further, as shown in FIG. 6, there is also provided a medical knife 51 having no second slanting surface. In the medical knife 51, a tip portion 55 having a sharp tip 54 is formed by causing first slanting surfaces 53 each composed of a flat surface and formed on both the sides of a blade portion 52 to be in coincidence with each other at the tip portion 55.
In the medical knife, which is disclosed in Japanese Patent Application Laid-Open No. 2001-238890, and the medical knife 51, the first and lower side slanting surfaces are formed as surfaces constituting cutting edges to dissect tissue and smoothly finished surfaces to reduce a resistance when tissue is dissected by the knives. The first slanting surface is formed by grinding such that it has an approximately constant width on the side from an extreme end to the widest portion.
In the respective medical knives arranged as described above, a piercing resistance is small when they pierce living body tissue as well as a resistance is also small when they dissect living body tissue. Accordingly, they can accurately dissect an affected area.
Although the medical knives, which have the sharp tip and the cutting edge formed in two directions from the tip to the widest portion, are advantageous in that they have the small piercing resistance when they pierce living body tissue, the medical knives are disadvantageous in that when they pierce living body tissue several times, the piercing resistance of them is increased, that is, they are poor in so-called durability. That is, since the blade portion of the medical knife has a very fine tip of about 1 (m, the tip is bent very easily. For example, even if the tip of the medical knife is slightly in touch with a cloth used in an operation, a finger, and the like before it pierces living body tissue, the cutting quality of the knife is deteriorated.
Further, when the medical knife 51 pierces living body tissue, in particular, the sclera, a hardened blood vessel, and the like of an eyeball, a large force acts on the sharp tip 54 through the piercing, and the tip portion 55 including the tip 54 is bent thereby as shown in, for example, FIG. 7, a problem also arises in that when it is intended to pierce living body tissue with the medical knife 51 whose tip portion 55 is bent, the piercing resistance is extremely increased.